generators — II. Physicochemical factors in the radiolytic reduction of pertechnetate

Heller-Grossman, Lily; Abrashkin, S.; Shafferman, Avigdor; Davis, Michael A.; Taube, Rebekah A.

doi:10.1016/0020-708x(81)90126-5

Cited by 10 publications

(7 citation statements)

References 13 publications

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“…Standard potentials of the possible reactions paths leading from TcO 4 - to TcO 2 · n H 2 O ( , ) are given in Figure . The one-electron reduction of TcO 4 - has been studied by electrochemical () and radiation chemical ( − ) methods. Taken together, these studies provide clear evidence for the formation of the Tc(VI) species TcO 4 2- .…”

Section: Resultsmentioning

confidence: 99%

Reduction of Pertechnetate by Ferrous Iron in Solution: Influence of Sorbed and Precipitated Fe(II)

Cui

Eriksen

1996

Environ. Sci. Technol.

137

129

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The reduction of TcO 4to TcO 2 ‚nH 2 O by Fe(II) in slightly acid to basic solution has been investigated in an all-glass reaction vessel with a hydrophobic inner surface. The three-electron reduction process, although thermodynamically feasible, was found to proceed very slowly if at all. Fe(II) sorbed on the wall of untreated reaction vessels or precipitated as Fe(OH) 2 (s) or FeCO 3 (s) was found to reduce TcO 4 -, the observed rates being proportional to the amount of sorbed or precipitated Fe(II). The experimental results are discussed in light of the standard redox potentials and possible reaction paths leading from TcO 4to TcO 2 ‚nH 2 O.

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Section: Resultsmentioning

confidence: 99%

Reduction of Pertechnetate by Ferrous Iron in Solution: Influence of Sorbed and Precipitated Fe(II)

Cui

Eriksen

1996

Environ. Sci. Technol.

137

129

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“…2). Namely, hydrated electrons play an important role for the reduction of TcO 4 − , as discussed for pulse radiolysis of TcO 4 − in the literature [8][9][10][11]. The TcO 2 ·nH 2 O colloids suddenly appeared at a higher dose (> 200 kGy) even in the N 2 O-saturated solution (Table 1).…”

Section: Reduction Processes Of Tco 4 −mentioning

confidence: 98%

“…All of these reports described that hexavalent technetium, Tc(VI), was produced by a bimolecular reaction of pertechnetate with hydrated electrons (e aq − ) at a rate constant of (1.3-2.5) × 10 10 M −1 s −1 . However, Deutsch et al [9] and Heller-Grossman et al [10] pointed out the appearance of brownish suspension or precipitate in the electron-irradiated solution at the pulse radiolysis experiments, suggesting the formation of hydrated technetium oxide (TcO 2 ·nH 2 O) as a result of further reduction of Tc(VI). Recently Said et al [12] observed a brown turbid solution by irradiation of aqueous pertechnetate solutions with 60 Co γ rays, and they concluded the formation of Tc(IV) colloids.…”

Section: Introductionmentioning

confidence: 97%

“…Radiolytic processes of Tc have mainly been investigated by pulse radiolysis of pertechnetate (TcO 4 − ) in aqueous solution [8][9][10][11]. All of these reports described that hexavalent technetium, Tc(VI), was produced by a bimolecular reaction of pertechnetate with hydrated electrons (e aq − ) at a rate constant of (1.3-2.5) × 10 10 M −1 s −1 .…”

Section: Introductionmentioning

confidence: 99%

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Radiolytic formation of Tc(IV) oxide colloids

Sekine¹,

Narushima²,

Kino³

et al. 2002

Radiochimica Acta

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Technetium(IV) oxide colloids were radiolytically formed by γ irradiation of aqueous solutions of pertechnetate (TcO 4 − ). Pertechnetate solutions (5.5 × 10 −5 -2.9 × 10 −4 M) were irradiated with bremsstrahlung from an electron linear accelerator at 40 and 17 • C. The color of irradiated solutions gradually changed to brownish black, suggesting the formation of Tc(IV) oxide colloids (TcO 2 ·nH 2 O). A transmission electron microscopy (TEM) analysis showed that the size of colloids distributed around 30 to 130 nm in diameter. The characteristic X-rays from technetium and oxygen were simultaneously detected from colloid particles at the TEM measurements. Roundshaped colloids were produced by irradiation at 40 • C, whereas irregular-shaped colloid particles composed of tiny particles (2 nm in diameter) were produced at 17 • C. The concentration of TcO 4 − in the target solution gradually decreased with an increase of the absorbed dose, corresponding to an increase of the colloid yield. The yield of colloids sharply increased in the solution deaerated by Ar bubbling before irradiation, but strongly suppressed in the solution saturated with oxygen (O 2 ) or nitrous oxide (N 2 O) gas. The fact suggests that hydrated electrons play an important role in the course of the reduction of TcO 4 − and that Tc(IV) oxide colloids were formed via successive disproportionation reactions of Tc(VI) and Tc(V). The formation mechanisms of Tc(IV) oxide colloids are discussed.

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“…The aqueous chemistry of technetium is likely to be dominated by the highly mobile pertechnetate anion (TcO 4 -) in aerobic waters, and by Tc(IV), as TcO 2 (am) solid, in anaerobic [2]. Under reducing conditions, TcO 4 -in non-complexing aqueous solutions initially undergoes a one-electron reduction to the unstable Tc VI O 4 2-species [3][4][5]. Subsequent two-or three-electron reductions to Tc(V) or Tc(IV) species then readily occur.…”

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confidence: 99%

The fate of Tc in a UK intermediate-level nuclear waste repository

Evans

Hallam

Aldridge

et al. 2008

WIT Transactions on Ecology and the Environment

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In the UK, tetraphenylphosphonium bromide (TPPB) has been used to remove technetium prior to disposal from some waste-streams by forming TPPBTc floc. If this floc were to be disposed of in a cementitious repository the TPPBTc would degrade by alkaline hydrolysis to triphenylphosphonium oxide, or by radiolysis to triphenylphosphine, releasing the Tc into solution. Its chemistry would be dominated by TcO 4 in aerobic waters and sparingly soluble TcO 2 (s) in anaerobic. Repository heterogeneity could mean that both Tc(VII) and Tc(IV) are present simultaneously. If TcO 4 -migrates into reducing conditions, ligands in the waste may complex with Tc during reduction to form water-soluble complexes. Also possible, is increased Tc solubility when organic ligands react with TcO 2 (s). Comparisons of Tc solubilities at high pH starting from TcO 2 and from TcO 4 -reduced in the presence of ligands were made. With EDTA and NTA no difference was observed, suggesting that Tc(IV)-ligand complexes were formed. For ISA and gluconic acid the Tc solubility starting from TcO 4 -was higher than in systems with TcO 2 as the starting point. This suggests that the TcO 4 -was not reduced to TcO 2 , but an intermediate oxidation state complex was formed, e.g. Tc(V). The conditional stability constant for the Tc(IV)-gluconic acid complex has been determined to be log β = 26.6 ± 0.2.

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generators — II. Physicochemical factors in the radiolytic reduction of pertechnetate

Cited by 10 publications

References 13 publications

Reduction of Pertechnetate by Ferrous Iron in Solution: Influence of Sorbed and Precipitated Fe(II)

Reduction of Pertechnetate by Ferrous Iron in Solution: Influence of Sorbed and Precipitated Fe(II)

Radiolytic formation of Tc(IV) oxide colloids

The fate of Tc in a UK intermediate-level nuclear waste repository

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